Compost Teas: Microbial Elixirs to Revive the Soil in Your Garden

Compost teas can significantly improve the health of your plants and the quality of the soil. These biologically active solutions are full of beneficial microorganisms, contain readily available nutrients and increase plant resistance to diseases. In this article you will learn how to prepare and apply compost teas and why they are an indispensable part of sustainable gardening.

Compost tea vs. worm tea: What is the difference?

Beginner growers and experienced gardeners often confuse compost tea and worm tea. At first glance these two types of organic extracts have much in common. Both worm and compost teas are produced as by-products of composting and are associated with ecological gardening and sustainable agriculture. So what are the differences between worm tea and compost tea?

Compost tea

Compost tea is a liquid made by extracting beneficial microorganisms (bacteria, fungi, nematodes and others) from compost through a steeping process. True compost tea contains all the organisms and soluble nutrients that were present in the compost before leaching. Depending on the preparation method we distinguish two types of compost teas – aerated and non-aerated.

• Aerated compost teas (ACT) are produced with a continuous supply of oxygen to the water, which supports the growth of beneficial aerobic bacteria.
• Non-aerated compost teas are made by simply soaking compost in water for a period of time without additional aeration.

Worm tea

Worm tea is the liquid that drains from home vermicomposters. This extract is rich in nutrients, but its composition differs significantly from compost tea. The content and balance of nutrients and microorganisms in vermicomposter leachate are strongly influenced by the materials the worms are fed and the conditions inside the bin. Worm tea can be useful, but it often contains more pathogens than well-prepared compost tea.

Benefits of compost tea

Compost teas are useful for both outdoor gardeners and indoor growers. They naturally support plant growth and improve overall plant health, vigor and nutrient uptake. Compost teas also improve soil structure by increasing microbial activity, which leads to faster decomposition of organic matter and release of nutrients into the substrate. In addition, beneficial microorganisms help plants defend more effectively against harmful pathogens. Thanks to easy preparation, application and low cost, compost teas are an ecological alternative to chemical fertilizers and pesticides, making them an excellent choice for growers practicing sustainable cultivation methods.

• Source of nutrients – During the steeping process important nutrients and minerals are released from the compost, making them immediately available to plants when applied to the soil or sprayed on leaves. Because of this, compost teas can be used as a versatile natural fertilizer with quick effects.
• Microbial life – One of the main advantages of compost teas is that they are literally full of beneficial bacteria, fungi, nematodes and other microbes. These microorganisms play a key role in the soil and the food web. Their primary task is breaking down organic matter into nutrients for plants.
• Disease suppression – Scientific studies have shown that compost tea can be effective at suppressing fungal and bacterial diseases that threaten plant health and can be used as an alternative to chemical treatments.
• Soil quality improvement – Regular application of compost tea improves soil structure and enhances its retention properties, i.e. aeration and the ability to hold water and nutrients. As a result, compost tea loosens clay soils and helps sandy soils retain water and nutrients better.

How to prepare compost tea

How to prepare compost tea

You can prepare your own compost tea either from a powder for preparing compost tea, worm humus or from your own compost. In the latter case, make sure it is well-matured compost that does not contain pathogen spores. Compost tea can be made with or without aeration and you can add supplementary high-sugar nutrients, such as molasses, which serve as food for the microbes. For best results we recommend choosing the aerated method, but the most important prerequisite for success is quality compost.

You will also need:

• Non-chlorinated or dechlorinated water – The effectiveness of compost tea depends on a thriving population of beneficial microbes. Chlorine and chloramine not only kill harmful pathogens in drinking water, they also harm these microbes. While chlorine is relatively unstable and gradually evaporates from water, chloramine must be neutralized using a carbon filter. If you are sure your tap water contains only chlorine, let it stand for 1–5 days in a dark cool place. You can speed up the process by aerating it with an air stone for 12–24 hours or by boiling the water.
• Container with an aeration system – For preparing compost tea for small or medium gardens a 10–20 liter bucket is suitable. A simple and effective aeration system can be assembled from an air pump, an air stone and some flexible tubing.
• Food for microbes – Adding molasses or a liquid additive for preparing compost tea will accelerate the reproduction of beneficial microbes in the mixture. Use additional sugars in moderation to avoid imbalance and the proliferation of anaerobic bacteria in the tea.

Step-by-step guide to preparing compost tea

• Preparing the compost: Start with quality, well-matured compost or a loose mix for preparing compost tea.
• Mixing and soaking: Fill the container with water and add compost at roughly a ratio of 1 part compost to 5 parts water or follow the product instructions.
• Aeration: Let the mixture steep for 24–48 hours, aerating it continuously and stirring several times.
• Straining and storage: After steeping, strain the mixture and use it as soon as possible, because at this time the tea contains the highest number of beneficial microbes.

Using compost tea

Compost tea can be applied directly to plant roots or sprayed on leaves; each of these methods has its advantages.

• Applying compost tea to plant roots: Simply pour fresh compost tea into the soil near the main stem of the plant. This method enriches the soil and delivers beneficial microorganisms and nutrients directly to the plant roots. Water plants with compost tea every two weeks throughout the growing season.
• Compost tea as a foliar spray: You can spray compost tea directly onto plant leaves, which provides an immediate effect in fighting pathogens. Apply sprays early in the morning or late afternoon to avoid leaf burn from the sun.

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